I earned a PhD before I was diagnosed but already had bipolar... have been for most of my life. Yes, some of the coursework feels like busy work but profs need a way to assess your learning so dig in and get it done as soon as you can. Your research and writing can be a challenge but also very interesting. I found that I did best in writing in blocks of time, such as writing my lit review during Christmas break. I went into a room, got rid of all distractions and went through every article I had found, mined for relevant information and then on to the next.

It is possible to earn a Ph.D. but I would agree with the others that if you drop out now you can lose credits and may not be accepted into another program as you may no longer viewed as a good candidate. If you want to teach at a university then stick with it. Be aware that tenure positions can be scarce, depending on your area and having dropped out and returned may not be viewed positively. So the question is, what do you want to do with your life?